Light emitting device and method for fabricating light emitting device

ABSTRACT

It is an object of the present invention to provide a method for fabricating a light emitting device, in which brightness gradient due to potential drop of a counter electrode can be prevented from being observed and an auxiliary electrode can be formed without increasing the number of steps, even when the precision of a light emitting device is improved. It is another object of the invention to provide a light emitting device fabricated according to the method. The light emitting device has a light emitting element and an auxiliary electrode in each pixel. The light emitting element includes a first electrode, a second electrode, an electroluminescent layer provided between the first and the second electrodes. Further, the first electrode is overlapped with the electroluminescent layer and the second electrode formed over an insulating film by means of a first opening formed in the insulating film. Still further, the auxiliary electrode is overlapped with the second electrode by means of a second opening formed over the second insulating film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device in which alight emitting element and an element for supplying current to the lightemitting element are provided for each of a plurality of pixels and to amethod for fabricating the light emitting device.

2. Description of the Related Art

A light emitting element has high visibility since it emits light byitself, and is most suitable for thinning since it does not need abacklight, which is required in a liquid crystal display device (LCD);further, there is no limitation of viewing angle either. Therefore, alight emitting device with the use of a light emitting element has beenattracting attention as a display device which replaces a CRT and anLCD. In late years, a light emitting device has been put to practicaluse; for example, it is provided in a cellular phone or an electronicdevice such as a digital still camera.

A light emitting element has an anode, a cathode, and anelectroluminescent layer sandwiched between the two electrodes. One ofthe two electrodes is referred to as a pixel electrode hereinafter. Inthe pixel electrode, the potential is controlled corresponding to avideo signal and a pixel electrode in a pixel is separated from pixelelectrodes in other pixels. The other electrode in which a commonpotential is given (referred to as a counter electrode) is normallyformed all over to be shared by all pixels, or formed so that pixels ofeach of RGB have a common counter electrode because it is not realisticto divide the counter electrode as the pixel electrode. Supply ofpotential to the counter electrode is performed via a connectionterminal provided at an end portion of a panel. Specifically, thecontact of the counter electrode with a wiring for leading (referred toas a leader wiring) is made, and the counter electrode and theconnection terminal are electrically connected by the leader wiring.Then, the contact is provided in a region other than an area where theelectroluminescent layer of a pixel area is formed.

As a screen is made larger, the area of the pixel area becomes larger,and potential drop due to the resistance of the counter electrode tendsto be significant. Brightness gradient could be observed when viewed asa whole pixel area since the absolute value of voltage Vel appliedbetween electrodes of a light emitting element is reduced in a pixel inwhich the potential drop of a counter electrode is significant. In orderto avoid the above problem, a technology is proposed in Reference 1(Reference 1: Japanese Patent Laid-Open No. 2002-033198). In thetechnology, an electrode for an auxiliary (an auxiliary electrode) isformed from a material with low resistance so that the auxiliaryelectrode is connected to a counter electrode, thereby uniforming thepotential in the plane of the counter electrode after the formation ofthe light emitting element.

As mentioned above, in the cases where the resistivity of a materialforming a counter electrode is high, or where the resistance of acounter electrode becomes high due to the increase in the area of apixel area, it is a very effective measure to form an auxiliaryelectrode for uniforming the potential in the plane of the counterelectrode. However, it is necessary to lay out the auxiliary electrodeso as to obstruct as less light from a light emitting element aspossible in the case of a type of a light emitting device (a topemission type) in which light emitted from an electroluminescent layeris released from a light transmitting counter electrode. However, evenif an auxiliary electrode is formed only in an area which is notoverlapped with a pixel area, it is difficult to obtain desirable effectof the uniform potential in the plane of the counter electrode.Therefore, an auxiliary electrode is formed over a counter electrode inthe area where light emission is not actually obtained, such as an areabetween light emitting elements of adjacent pixels.

However, as the size of a pixel is reduced due to developments in higherprecision of pixels as well as larger screens, the width between lightemitting elements of adjacent pixels becomes less than 20 μm.Accordingly, an auxiliary electrode is required to fit within the abovewidth, and it is becoming difficult to form an auxiliary electrode overa counter electrode by vapor deposition with the use of a metal maskwhich cannot form a very precise pattern. When an auxiliary electrode isformed over a counter electrode by photolithography, the pattern can beformed with precision of μm or less. However, it is unfavorable sincedegradation of a light emitting element due to light or moisture mightbe accelerated in serial steps including exposure, development, andremoval of a photoresist. Further, although an auxiliary electrode canbe formed by a printing method typified by ink-jet printing, it isundesirable since the number of steps for forming the auxiliaryelectrode would increase. This problem is the same in vapor depositionand lithography.

SUMMARY OF THE INVENTION

In view of the above problem, it is an object of the present inventionto provide a method for fabricating a light emitting device, in whichbrightness gradient due to potential drop of a counter electrode can beprevented from being observed and an auxiliary electrode can be formedwithout increasing the number of steps, even when the precision of alight emitting device is improved. It is another object of the inventionto provide a light emitting device fabricated according to the method.

According to the invention, an auxiliary electrode is formed before theformation of an electroluminescent layer of a light emitting elementrather than after. An auxiliary electrode is formed before the formationof an electroluminescent layer; accordingly, the auxiliary electrode canbe formed by photolithography. Further, a precise pattern can be formedby using photolithography. Thus, even if the width between lightemitting elements is reduced to less than 20 μm due to the highprecision, the auxiliary electrode can be formed to fit within thewidth. In addition, according to the invention, the auxiliary electrodeis formed by photolithography together with a wiring and a gateelectrode formed from a conductive film in a pixel area, thereby formingan auxiliary electrode without increasing the number of steps.

The auxiliary electrode can suppress the potential drop of a counterelectrode and prevent brightness gradient from being observed in a pixelarea. The invention is particularly effective in a light emitting deviceof the top emission type whose auxiliary electrode is difficult to beformed all over the counter electrode.

In the invention, an auxiliary electrode makes contact with a counterelectrode of a light emitting element in a pixel area, although anelectroluminescent layer is normally formed between a counter electrodeand a pixel electrode in a pixel area. The electroluminescent layerincludes a hole injection layer, a hole transport layer, a lightemitting layer, an electron injection layer, an electron transportlayer, and the like. The light emitting layer particularly hassignificantly high resistance compared with an auxiliary electrode or acounter electrode. Then, in the invention, the contact is formed byturning into advantage the weakness of inferiority in the step coverageof a light emitting layer in the end portion of the auxiliary electrode,which is caused since the thickness of the auxiliary electrode isthinner compared with that of the light emitting layer. Namely, anauxiliary electrode and a counter electrode are electrically connectedin an area which is not covered with the light emitting layer due to theinferiority in step coverage. Note that a hole injection layer, a holetransport layer, an electron injection layer, an electron transportlayer, and the like that are formed from materials with relatively lowresistance compared with a light emitting layer may be provided betweenthe auxiliary electrode and the counter electrode, thereby electricallyconnecting the auxiliary electrode and the counter electrode. Further,the film thickness of the auxiliary electrode may be set thicker thanthe film thickness of the whole electroluminescent layer, so that thecoverage of the electroluminescent layer in the end portion of theauxiliary electrode is reduced; thus, the counter electrode and theauxiliary electrode have a direct contact with each other.

The method for connecting an auxiliary electrode and a counter electrodeaccording to the invention is not limited to the method using the stepcoverage. Alternatively, when a light emitting layer is formed by vapordeposition using a metal mask, it is another option to form an areawhere the light emitting layer is not formed and to electrically connectthe auxiliary electrode to the counter electrode. In the case of a fullcolor display light emitting device which is fabricated by separatelyapplying light emitting layers corresponding to each color of the threeprimary colors using a metal mask, the area where a light emitting layeris not formed can be formed by using the metal mask; thus, the contactcan be made by employing the above method without increasing the numberof steps.

In this specification, a light emitting device includes a panel in whicha light emitting element is sealed and a module in which an IC having acontroller and the like are mounted on the panel.

Further, an electroluminescent layer has a single layer or a pluralityof layers, and an inorganic compound may be included therein. Theluminescence in the electroluminescent layer includes luminescence thatis generated when an singlet excited state returns to a ground state(fluorescence) and luminescence that is generated when an triplet exitedstate returns to a ground state (phosphorescence).

According to the invention, an auxiliary electrode can be formed byusing a photolithography since the auxiliary electrode is formed beforeforming a light emitting element. Further, a precise pattern can beformed by using the photolithography. Accordingly, even if the widthbetween light emitting elements is reduced to less than 20 μm due to thehigh precision, the auxiliary electrode can be formed to fit within thewidth. Further, according to the invention, the auxiliary electrode isformed by photolithography as the same as wirings of a pixel area, agate electrode, and the like that are formed from a conductive film;thus, the auxiliary electrode can be formed without increasing thenumber of steps. The auxiliary electrode can suppress the potential dropof a counter electrode and prevent brightness gradient from beingobserved in a pixel area. The invention is particularly effective in alight emitting device of the top emission type whose auxiliary electrodeis difficult to be formed all over the counter electrode.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a figure showing a configuration of a pixel area in a lightemitting device of the invention.

FIGS. 2A to 2C are cross-sectional views of a pixel area shown in FIG.1.

FIG. 3 is a figure showing a configuration of a pixel area in a lightemitting device of the invention.

FIGS. 4A to 4C are cross-sectional views of a pixel area in a lightemitting device of the invention.

FIGS. 5A to 5C are cross-sectional views of a pixel area in a lightemitting device of the invention.

FIGS. 6A to 6C are cross-sectional views of a pixel area in a lightemitting device of the invention.

FIGS. 7A to 7C are cross-sectional views of a pixel area in a lightemitting device of the invention.

FIGS. 8A to 8C are cross-sectional views of a pixel area in a lightemitting device of the invention.

FIG. 9 is a figure showing a configuration of a pixel area in a lightemitting device of the invention.

FIGS. 10A to 10C are cross-sectional views of a pixel area shown in FIG.9.

FIG. 11 is a figure showing a configuration of a connecting portionbetween an auxiliary wiring and a counter electrode in a light emittingdevice of the invention.

FIG. 12 is a figure showing a configuration of a light emitting deviceof the invention.

FIGS. 13A and 13B are schematic diagrams of a pixel area in a lightemitting device of the invention.

FIG. 14 is a schematic diagram of a pixel area in a light emittingdevice of the invention.

FIG. 15 is a figure showing a layout of leader wiring and connectionwiring in a light emitting device of the invention.

FIGS. 16A to 16D are schematic diagrams of a pixel in a light emittingdevice of the invention.

FIGS. 17A to 17D are schematic diagrams of a pixel in a light emittingdevice of the invention.

FIG. 18 is a top view of a pixel in a light emitting device of theinvention.

FIGS. 19A and 19B are cross-sectional views of a pixel in a lightemitting device of the invention.

FIGS. 20A and 20B are cross-sectional views of a pixel in a lightemitting device of the invention.

FIG. 21 is a cross-sectional view of a pixel in a light emitting deviceof the invention.

FIGS. 22A and 22B are cross-sectional views of a pixel in a lightemitting device of the invention.

FIGS. 23A and 23B are cross-sectional views of a pixel in a lightemitting device of the invention.

FIG. 24 is a cross-sectional view of a pixel in a light emitting deviceof the invention.

FIGS. 25A and 25B are a top view and a cross-sectional view of a lightemitting device of the invention.

FIGS. 26A to 26E are figures showing electronic devices each using alight emitting device of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes of the present invention will be described withreference to the accompanying drawings. Note that the present inventioncan be implemented in various modes, and it is understood easily bythose skilled in the art that embodiment modes and details of theinvention can be variously changed without departing from the spirit andscope of the invention. Therefore, the present invention is notconstrued with a limitation on the contents of the embodiment modes.

Embodiment Mode 1

The configuration of a pixel area in a light emitting device of thisembodiment mode will be described with reference to FIG. 1. FIG. 1 showsa top view of a pixel area and a leader wiring. Reference numeral 301denotes a connection terminal, and reference numerals 302 a, 302 b, and302 c denote leader wirings. Further, an electrode 303 formed in thepixel area is equivalent to an auxiliary electrode, and the electrode isconnected to the connection terminal 301 via the leader wirings 302 a,302 b, and 302 c. In FIG. 1, the connection terminal 301 and theauxiliary electrode 303 are electrically connected by using the threeleader wirings of 302 a, 302 b, and 302 c. However, the configuration ofleader wirings is not limited to the configuration shown in FIG. 1, andany configuration may be used as long as the connection terminal 301 andthe auxiliary electrode 303 can be connected electrically. All of aconnection terminal, a leader wiring, and an auxiliary electrode may beformed from one conductive film.

A plurality of wirings are provided in the pixel area; specifically inthis embodiment mode, the pixel area has a scan line 306 for selecting apixel, a signal line 304 for supplying a video signal to the selectedpixel, and a power line 305 for supplying current to a light emittingelement. Note that wirings to be provided in the pixel area of theinvention is not limited to the three wirings, and some other wiringsthan the above wirings may be provided depending on the pixel structure.

Further, in this embodiment mode, in a step for forming the signal line304 and the power line 305 by patterning one conductive film, theauxiliary electrode 303 is also formed. With the above structure, nomore steps are required for forming the auxiliary electrode 303. Theauxiliary electrode 303 is not necessarily formed from the conductivefilm for forming the signal line 304 and the power line 305. Theauxiliary electrode 303 may be formed in a step for forming anotherwiring for example, a scan line 306, aside from the signal line 304 andthe power line 305.

As in this embodiment mode, when the signal line 304 and the power line305 are formed from the same conductive film as the leader wiring 302 c,the signal line 304 and the power line 305 are connected to a wiring 315formed in another layer so as to pass under the leader wiring 302 c;thus, the signal line 304 and the power line 305, and the leader wiring302 c can be crossed so as not to contact each other.

In FIG. 1, reference numeral 307 denotes a pixel electrode (a firstelectrode), and an electrode in one pixel is separated from those in theother pixels. An electroluminescent layer corresponding to each color isformed in each of a plurality of areas shown by dashed lines 309.Further, a counter electrode (a second electrode) is formed in an areashown by dashed lines 310, and an electroluminescent layer 309 issandwiched between the pixel electrode 307 and the counter electrode310. In this embodiment mode, an example in which an anode is used as apixel electrode, and a cathode is used as a counter electrode is shown;however, the invention is not limited to the configuration. The cathodemay be used as a pixel electrode, and the anode may be used as a counterelectrode.

In FIG. 1, the leader wiring 302 a is connected to one end portion of aresistor 334 formed from a semiconductor film, and the other end of theresistor 334 is electrically connected to a connection terminal 330 viaa wiring 331. Noise of a signal inputted into the connection terminal301 can be reduced, and the subsequent circuit element can be preventedfrom being damaged by static electricity or the like by providing theresistor 334.

A cross-sectional view of A-A′ in FIG. 1 is shown in FIG. 2A. Across-sectional view of B-B′ in FIG. 1 is shown in FIG. 2B. Across-sectional view of C-C′ in FIG. 1 is shown in FIG. 2C. As shown inFIG. 2A, a wiring 311 (hereinafter referred to as a connection wiring)for giving potential to the pixel electrode 307 depending on a videosignal inputted into a pixel is provided as well as the signal line 304,the power line 305, and the auxiliary electrode 303 over a firstinterlayer insulating film (a first insulating film) 312. Further, thepixel electrode 307 is formed over the connection wiring 311. Thecounter electrode 310 is formed from a light transmitting electrode, andlight generated in the electroluminescent layer 309 reflects off theconnection wiring 311; thus, the light can be released from the side ofthe counter electrode 310.

As in this embodiment mode, in the case of a top emission light emittingdevice, a light transmitting cathode is used for the counter electrode310. Specifically, an electrode having a film thickness thin enough totransmit the light generated in the electroluminescent layer is used.Preferably, the film thickness is approximately 5 nm to 30 nm. Further,a transparent conductive film 316 which transmits light is formed so asto cover the counter electrode 310 in this embodiment mode. Even if theresistance of the counter electrode 310 itself is increased by thinningthe thickness thereof, potential drop can be suppressed by providing thetransparent conductive film 316. However, the transparent conductivefilm 316 is not necessarily provided.

In this embodiment mode, the configuration in which light emitted froman electroluminescent layer is released from the counter electrode sideis described; however, the invention is not limited to theconfiguration. A type in which light is released from the pixelelectrode side (a bottom emission type) or a type in which light isreleased from both the counter electrode side and the pixel electrodeside (a dual emission type) may be used.

A second interlayer insulating film (a second insulating film) 313 isformed over the first interlayer insulating film 312 so as to cover theend portion of the pixel electrode 307, the signal line 304, the powerline 305, the end portion of the leader wiring 302 c, and the endportion of the auxiliary electrode 303. The second interlayer insulatingfilm 313 has openings 308 a and 308 b. A part of the pixel electrode307, a part of the leader wiring 302 c, and a part of the auxiliaryelectrode 303 are exposed in the openings 308 a and 308 b. In theopening 308 a, the pixel electrode 307, the electroluminescent layer309, and the counter electrode 310 are overlapped with each other, thusforming the light emitting element 314.

In this embodiment mode, when an electroluminescent layer correspondingto each color of the three primary colors is formed by vapor depositionusing a metal mask, an area where the light emitting layer is not formedis formed, and the auxiliary electrode and the counter electrode areelectrically connected in the area. Specifically, the opening 308 b andthe area where the electroluminescent layer 309 is formed are madecompletely not to overlap, or to overlap only partially. In other words,the counter electrode 310 is to be formed in a state where the auxiliaryelectrode 303 is exposed completely or partially in the opening 308 b.With the above structure, the auxiliary electrode 303 can be connectedto the counter electrode 310 in the opening 308 b. Further in thisembodiment mode, the electrical connection between the counter electrode310 and the auxiliary electrode 303 can be made more firm by forming thetransparent conductive film 316 so as to cover the counter electrode310. With the above structure, the auxiliary electrode 303 can beconnected to the counter electrode 310 in the pixel area.

Meanwhile, the electroluminescent layer 309 is not formed between theleader wiring 302 c and the counter electrode 310. Accordingly, as shownin FIG. 2B, the leader wiring 302 c and the counter electrode 310 areconnected in the opening 308 b. Further, the power supply potentialsupplied from the connection terminal 301 is supplied to the auxiliaryelectrode 303 and the counter electrode 310 through the leader wiring302 c. The potential drop of the counter electrode 310 can be suppressedand brightness gradient can be prevented from being observed in thepixel area by using the auxiliary electrode 303. The invention isparticularly effective in a light emitting device of the top emissiontype whose auxiliary electrode is difficult to be formed all over thecounter electrode.

According to the invention, an auxiliary electrode is formed before theformation of a light emitting layer, so that the auxiliary electrode canbe formed by photolithography. Further, a precise pattern can be formedby using photolithography. Accordingly, even if the width between lightemitting elements is reduced to less than 20 μm due to the highprecision, the auxiliary electrode can be formed to fit within thewidth. Further, according to the invention, the auxiliary electrode isformed by photolithography as the same as a wiring of a pixel area or agate electrode that are formed from one conductive film; thus, theauxiliary electrode can be formed without increasing the number ofsteps.

Note that, in this embodiment mode, the leader wiring 302 c and theauxiliary electrode 303 are connected to the counter electrode 310 inthe one opening 308 b. The shape of the opening is not limited to thisembodiment mode. An opening for exposing the leader wirings 302 a, 302b, and 302 c and an opening for exposing the auxiliary electrode 303 maybe separated, or a plurality of openings for exposing the auxiliaryelectrode 303 may be provided.

Further, in this embodiment mode, a case where an electroluminescentlayer of one color is separated from those of other colors is described.However, at least a light emitting layer should be separated, and a holeinjection layer, a hole transport layer, an electron injection layer,and an electron transport layer that are formed from materials withrelatively low resistance compared with the light emitting layer may notbe necessarily separated. In this case, the counter electrode can beelectrically connected to the auxiliary electrode via one of a boleinjection layer, a hole transport layer, an electron injection layer,and an electron transport layer.

As in this embodiment mode, in the case of a full color display lightemitting device which is fabricated by separately coloring a lightemitting layer corresponding to each color of the three primary colorsusing a metal mask, the area where light emitting layer is not formedcan be formed by using the metal mask; thus, the contact can be madewithout increasing the number of steps by employing the above method.Note that the electroluminescent layer formed in the opening may beselectively removed by plasma etching using a metal mask, and one ormore gases selected from Ar, H, F, and O as an etching gas.

Embodiment Mode 2

In this embodiment mode, a mode of a shape of an opening, which isdifferent from the one in Embodiment Mode 1 will be described.

FIG. 3 shows a top view of a pixel area in this embodiment mode.Reference numeral 403 denotes an opening, and a counter electrode 404and an auxiliary electrode 401 are electrically connected in an opening403. In this embodiment mode, when an electroluminescent layer 405 isformed so as not to entirely cover the opening 403 by using a metalmask; thus, the auxiliary electrode 401 is connected to the counterelectrode 404 directly or electrically in the opening 403. In this case,the end portion of the auxiliary electrode may be exposed in theopening, or may be covered with a second interlayer insulating film.

The end portion of the auxiliary electrode 401 may be exposed in theopening 403, and a part which is not covered by the electroluminescentlayer 405 may be deliberately provided in the end portion by means ofcoverage thereby connecting the counter electrode 404 and the auxiliaryelectrode 401.

A leader wiring 406 is partially exposed in an opening 402. Since theopening 402 is not overlapped with the electroluminescent layer 405, theleader wiring 406 and the counter electrode 404 are connected in theopening 402.

Reference numeral 407 denotes a pixel electrode provided for each pixel.Further, the pixel electrode 407, the electroluminescent layer 405, andthe counter electrode 404 are overlapped in an opening 408, and thus, alight emitting element is formed.

As shown in FIG. 3, short-circuit between the opening 408 and anotheradjacent wiring with the misalignment of a mask in forming the openings403 and 408 can be inhibited by arranging the openings 403 at the fourcorners of the opening 408 where each light emitting element is formed.

Embodiment Mode 3

In this embodiment mode, a mode in which a structure of a portion wherean auxiliary electrode and a counter electrode are connected isdifferent from that of Embodiment Mode 1 will be described.

The configuration of a pixel area in a light emitting device of thisembodiment mode will be described with reference to FIG. 9. FIG. 9 showsa top view of a pixel area and a leader wiring. Reference numeral 101denotes a connection terminal, 102 a, 102 b, 102 c denote leaderwirings, and 103 denotes an auxiliary electrode. As in FIG. 1, theauxiliary electrode 103 is electrically connected to the connectionterminal 101 via leader wirings 102 a, 102 b, and 102 c.

As in Embodiment Mode 1, a scan line 106, a signal line 104, and a powerline 105 are provided in the pixel area. The wirings to be provided inthe pixel area of the invention is not limited to the three wirings, andsome other wirings than the above wirings may be provided depending onthe pixel structure. Further, as in Embodiment Mode 1, in thisembodiment mode, the auxiliary electrode 101 is formed in a step forforming the signal line 104 and the power line 105 by patterning oneconductive film. With the above structure, no more steps are requiredfor forming the auxiliary electrode 103. Note that it is not necessarilyneeded that the auxiliary electrode 103 is formed by patterning the sameconductive electrode as the signal line 104 and the power line 105. Theauxiliary electrode 103 may be formed in a step for forming anotherwiring, for example, a scan line, aside from the signal line 104 and thepower line 105.

In FIG. 9, reference numeral 107 denotes a pixel electrode. In thisembodiment mode, an electroluminescent layer is formed in an area shownby dashed lines 109. Further, a counter electrode is formed in an areashown by dashed lines 110, and the electroluminescent layer 109 issandwiched between the pixel electrode 107 and the counter electrode110.

In FIG. 9, the leader wiring 102 a and one end of a resistor 134 formedfrom a semiconductor film are connected, and the other end of theresistor 134 is electrically connected to a connection terminal 130 viaa wiring 131. Noise of a signal inputted into the connection terminal101 can be reduced, and a subsequent circuit element can be preventedfrom being damaged due to static electricity or the like by providingthe resistor 134.

A cross-sectional view of A-A′ in FIG. 9 is shown in FIG. 10A. Across-sectional view of B-B′ in FIG. 9 is shown in FIG. 10B. As shown infigure FIG. 10A, a wiring 111 is provided as well as the signal line104, the power line 105, and the auxiliary electrode 103 are formed overa first interlayer insulating film 112, and the pixel electrode 107 isformed on the connection wiring 111 as in Embodiment Mode 1. Further,the counter electrode 110 is formed from a light transmitting electrode,and light generated in the electroluminescent layer 109 reflects off theconnection wiring 111; thus, the light can be released from the side ofthe counter electrode 110.

A second interlayer insulating film 113 is formed over the firstinterlayer insulating film 112 so as to cover the end portion of thepixel electrode 107, the signal line 104 and the power line 105. Thesecond interlayer insulating film 113 has openings 108 a and 108 b. Apart of the pixel electrode 107, a part of the leader wiring 102, andthe auxiliary electrode 103 are exposed in the openings 108 a and 108 b.In the opening 108 a, the pixel electrode 107, the electroluminescentlayer 109, and the counter electrode 110 are overlapped with each other,thus forming a light emitting element 114. Note that, in FIG. 9, the endportion of the auxiliary electrode 103 is not exposed in the opening 108b and covered with the second interlayer insulating film 113; however,this embodiment mode is not limited to the configuration. The endportion of the auxiliary electrode 103 may be exposed.

In the opening 108 b, the electroluminescent layer 109 is formed in astate where the end portion of the auxiliary electrode 103 is exposedwithout being covered with the second interlayer insulating film 113.Accordingly, when the electroluminescent layer 109 is formed by vapordeposition, the auxiliary electrode 103 is partially but not completelycovered with the electroluminescent layer 109; thus, the uncoveredportion is connected to the counter electrode 110.

In FIG. 11, an enlarged view of a portion where the auxiliary electrode103 and the counter electrode 110 are connected is shown. In thisembodiment mode as shown in FIG. 11, when the electroluminescent layer109 is formed by vapor deposition, the auxiliary electrode 103 is formedto be covered partially but not completely. The counter electrode 110 isformed thereafter, so that the exposed end portion of the auxiliaryelectrode 103 and the counter electrode 110 are connected as shown inthe area 120 enclosed by dashed lines. Further in this embodiment mode,the electrical connection between the counter electrode 110 and theauxiliary electrode 103 can be made more firm by forming the transparentconductive film 116 so as to cover the counter electrode 110. With theabove structure, the auxiliary electrode 103 can be connected to thecounter electrode 110 in the pixel area.

In this embodiment mode, an example in which an anode is used as a pixelelectrode, and a cathode is used as a counter electrode is shown;however, the invention is not limited to the configuration. The cathodemay be used as a pixel electrode, and the anode may be used as a counterelectrode. Further, in this embodiment mode, a top emission lightemitting device is employed. As in Embodiment Mode 1, a lighttransmitting electrode is used for the counter electrode 110, and atransparent conductive film 116 which transmit light is formed so as tocover the counter electrode 110. Even if the resistance of the counterelectrode 110 itself is increased by thinning the thickness thereof,potential drop can be suppressed by providing the transparent conductivefilm 116. However, the transparent conductive film is not necessarilyprovided.

In this embodiment mode, the configuration in which light emitted froman electroluminescent layer is released from the counter electrode sideis described; however, the invention is not limited to theconfiguration. A type in which light is released from the pixelelectrode side (a bottom emission type) or a type in which light isreleased from both the counter electrode side and the pixel electrodeside (a dual emission type) may be used.

Meanwhile, the electroluminescent layer 109 is not formed between theleader wiring 102 and the counter electrode 110. Accordingly, as shownin FIG. 2B, the leader wiring 102 and the counter electrode 110 areconnected in the opening 108 b. Further, the power supply potentialsupplied from the connection terminal 101 is supplied to the auxiliaryelectrode 103 and the counter electrode 110 through the leader wiring102. The potential drop of the counter electrode 110 can be suppressedand brightness gradient can be prevented from being observed in thepixel area by using the auxiliary electrode 103. The invention isparticularly effective in a light emitting device of the top emissiontype whose auxiliary electrode is difficult to be formed all over thecounter electrode.

In this embodiment mode, an auxiliary electrode is exposed, and theauxiliary electrode and a counter electrode are connected by making useof the coverage characteristics of an electroluminescent layer. However,the invention is not limited thereto. The area where anelectroluminescent layer is not formed is formed in the pixel area, andan auxiliary electrode may make contact with a counter electrode in thearea. Further, in this embodiment mode, a case where anelectroluminescent layer is wholly formed by vapor deposition isdescribed; however, at least a light emitting layer should be formed byvapor deposition, and a hole injection layer, a hole transport layer, anelectron injection layer, an electron transport layer, and the like thatare formed from materials with relatively low resistance compared withthe light emitting layer may be formed by an application method withoutlimitation to vapor deposition. In this case, the auxiliary electrodeand the counter electrode can be electrically connected via a holeinjection layer, a hole transport layer, an electron injection layer, oran electron transport layer in the area where a light emitting layer isnot formed in the end of an auxiliary electrode.

According to the invention, an auxiliary electrode can be formed byusing a photolithography since the auxiliary electrode can be formedbefore forming a light emitting element. Further, a precise pattern canbe formed by using the photolithography. Accordingly, even if the widthbetween light emitting elements is reduced to less than 20 μm due to thehigh precision, the auxiliary electrode can be formed to fit within thewidth. Further, according to the invention, the auxiliary electrode isformed by photolithography as the same as wirings of a pixel area, agate electrode, and the like that are formed from a conductive film;thus, the auxiliary electrode can be formed without increasing thenumber of steps.

Note that, in this embodiment mode, the leader wiring 102 and theauxiliary electrode 103 are connected to the counter electrode 110 inthe one opening 108 b; however, the shape of the opening is not limitedto this embodiment mode. An opening for exposing the leader wiring 102and an opening for exposing the auxiliary electrode may be separated, ora plurality of openings for exposing the auxiliary electrode may beprovided.

Embodiment Mode 4

In this embodiment mode, a mode of a light emitting element included ina light emitting device of the invention will be described. FIG. 4Ashows a cross-sectional view of a pixel of this embodiment mode.Enlarged views of a portion which is enclosed by dashed lines 570 and aportion enclosed by dashed lines 571 in FIG. 4A are respectively shownin FIG. 4B and FIG. 4C.

In FIG. 4A, a base film 501 is formed over a substrate 500, and atransistor 502 which controls supply of current to a light emittingelement (a driver transistor) is formed over the base film 501. Thedriver transistor 502 includes an active layer 503, a gate electrode505, and a gate insulating film 504 sandwiched between the active layer503 and the gate electrode 505.

It is preferable to use a polycrystalline semiconductor film for theactive layer 503, and the polycrystalline semiconductor film can beformed by crystallizing an amorphous silicon film by a known technology.As the known technology of crystallization, thermo-crystallization usingan electrically heated furnace, laser annealing crystallization using alaser beam, and a lamp annealing crystallization using infrared lightare given. In this embodiment mode, the crystallization is performed byan excimer laser beam using XeCl gas. It should be noted that a pulsedexcimer laser beam which is shaped into a linear beam is used in thisembodiment mode; however, the excimer laser beam may be rectangular, ora continuous-wave argon laser beam or a continuous-wave excimer laserbeam can also be used. Alternatively, the polycrystalline semiconductorfilm may be formed by a crystallization method using a catalytic elementaccording to a technique described in Japanese Patent Laid-Open No. Hei07-130652. Further, a polycrystalline semiconductor film formed bysputtering, PCVD, thermal CVD, or the like may be used.

As for the active layer, silicon germanium can be used instead ofsilicon. When silicon germanium is used, the concentration of germaniumis preferably set at approximately from 0.01 atomic % to 4.5 atomic %.Further, silicon added with carbon nitride may be used.

The gate insulating film 504 can use silicon oxide, silicon nitride, orsilicon oxynitride. Further, a layered film of the compounds, forexample, a film in which SiN is stacked on SiO₂ may be used as the gateinsulating film. TEOS (tetraethyl orthosilicate) and O₂ are mixed inplasma CVD, and discharged under the following conditions: reactionpressure of 40 Pa, the substrate temperature from 300° C. to 400° C.,high frequency of 13.56 MHz, and the power density in a range of 0.5W/cm² to 0.8 W/cm², thereby forming a silicon oxide film. Then, thesilicon oxide film thus prepared can obtain excellent characteristics asa gate insulating film by thermo-annealing at a temperature from 400° C.to 500° C. Further, aluminum nitride may be used for the gate insulatingfilm. Aluminum nitride has relatively high thermal conductivity, it caneffectively diffuse the heat generated at a TFT. Furthermore, aftersilicon oxide, silicon oxynitride, or the like which does not containaluminum is formed, aluminum nitride may be stacked thereover to be usedas a gate insulating film. Alternatively, SiO₂ formed by RF sputteringusing Si as a target may be used for the gate insulating film.

The gate electrode 505 is formed from an element selected from Ta, W,Ti, Mo, Al and Cu, or an alloy material or a compound materialcontaining the above elements as major components. A semiconductor filmtypified by a polycrystalline silicon film into which an impurityelement such as phosphorus has been doped may also be used. Moreover, itmay be a laminate of a plurality of conductive films instead of a singleconductive film.

For example, the following combinations are preferable: a firstconductive film is formed from tantalum nitride (TaN) and a secondconductive film is formed from W; the first conductive film is formedfrom tantalum nitride (TaN) and the second conductive film is formedfrom Ti; the first conductive film is formed from tantalum nitride (TaN)and the second conductive film is formed from Al; and the firstconductive film is formed from tantalum nitride (TaN) and the secondconductive film is formed from Cu (copper). Moreover, a semiconductorfilm typified by a polycrystalline silicon film in which an impurityelement such as phosphorus has been doped, or Ag—Pd—Cu alloy may also beused for the first conductive film and the second conductive film.

The structure of the conductive film is not limited to the two-layerstructure; for example, a three-layer structure in which a tungstenfilm, an alloy film containing aluminum and silicon (Al—Si), and atitanium nitride film are stacked in sequence may be used. Further, inthe case of the three-layer structure, tungsten nitride may be usedinstead of tungsten; an alloy film of aluminum and titanium (Al—Ti) maybe used instead of an alloy film of aluminum and silicon (Al—Si); or atitanium film may be used instead of a titanium nitride film. Note thatit is important to select the most suitable method of etching, and akind of an etchant depending on materials of the conductive film.

The driver transistor 502 is covered with a first interlayer insulatingfilm 507, and a passivation film 508 is stacked over the firstinterlayer insulating film 507.

The first interlayer insulating film 507 can use non-photosensitiveacrylic, an oxide film, or a silicon oxynitride film. The passivationfilm 508 uses a film which hardly transmits a substance which mayaccelerate deterioration of a light emitting element, such as moistureor oxygen, compared with other insulating films. Typically, a DLC film,a carbon nitride film, a silicon nitride film formed by RF sputtering,or the like is desirably used for the passivation film. Further, thepassivation film 508 can prevent alkali metal, alkaline earth metal, ortransition metal contained in an electron injection layer 513 fromleaking out of the panel.

A connection wiring 506 is formed over the passivation film 508, and thedriver transistor 502 is connected to the connection wiring 506 througha contact hole. Further, an auxiliary electrode 520 which is obtained bypatterning a conductive film from which the connection wiring 506 isalso formed is formed over the passivation film 508.

Reference numeral 510 denotes a pixel electrode, 511 denotes a holeinjection layer, 512 denotes a light emitting layer, and 513 denotes anelectron injection layer. The pixel electrode 510 is formed on theconnection wiring 506, and a second interlayer insulating film 523having openings 521 and 522 for exposing a part of the pixel electrode510 and a part of the auxiliary electrode 520 is formed over thepassivation film 508. Further, the hole injection layer 511, the lightemitting layer 512, and the electron injection layer 513 are formed insequence so as to cover the passivation film 508 and the opening 521.

In this embodiment mode, the pixel electrode 510, the hole injectionlayer 511, the light emitting layer 512, and the electron injectionlayer 513 overlap in the opening 521, and the overlapping portion isequivalent to a light emitting element 514. Note that the light emittinglayer 512 is formed by using a metal mask 572 so as not to cover theopening 522 completely and to expose the auxiliary electrode 520partially. Accordingly, the hole injection layer 511 and the electroninjection layer 513 are sequentially stacked over the auxiliaryelectrode 520 in the opening 522. The portion where the pixel electrode510, the hole injection layer 511, the light emitting layer 512, and theelectron injection layer 513 overlap is equivalent to the light emittingelement 514.

In this embodiment mode, a polyethylene dioxythiophene-polystyrenesulfonate (PEDOT/PSS) thin film, for example, can be formed for the holeinjection layer 511 by an application method.

The electron injection layer of this embodiment uses an electroninjection composition in which molar ratio of a benzoxazole derivativeand one of an alkali metal, an alkaline earth metal, and a transitionmetal (for example, Li, Mg, Cs, or the like) is from 1:0.1 to 1:10. Andthe electron injection layer 513 having the above structure is usedinstead of a counter electrode. In this embodiment mode, the molar ratioof the benzoxazole derivative represented by the formula 1 to Li, thatis an alkali metal, is made to be 2:1 thereby forming the electroninjection layer with a film thickness of 20 nm by co-evaporation.

-   -   4,4′-Bis(5-methyl benzoxazol-2-yl)stilbene

Over the electron injection layer 513, a protective film 524 is formed.As with the passivation film 508, the protective film 524 is formed witha film which hardly transmits a substance which may acceleratedeterioration of a light emitting element, such as moisture or oxygen,compared with other insulating films. Typically, a DLC film, a carbonnitride film, a silicon nitride film formed by RF sputtering, or thelike is desirably used for the protective film 508. A laminate of thefilm which hardly transmits substances such as moisture and oxygen, anda film which transmits substances such as moisture and oxygen easilycompared with the above film may also be used for the protective film.

The second interlayer insulating film 523 is heated in a vacuumatmosphere in order to remove absorbed moisture and oxygen beforeforming the hole injection layer 511, the light emitting layer 512, andthe electron injection layer 513. Specifically, heat treatment isapplied in a vacuum atmosphere, at a temperature from 100° C. to 200° C.and for approximately 0.5 to 1 hour. The pressure is desirably set at3×10⁻⁷ Torr or less, and if possible at 3×10⁻⁸ Torr or less. In the casewhere the hole injection layer 511, the light emitting layer 512, andthe electron injection layer 513 are formed after performing the heattreatment to the second interlayer insulating film 523 in the vacuumatmosphere, the reliability can be further improved by keeping the holeinjection layer 511, the light emitting layer 512, and the electroninjection layer 513 under the vacuum atmosphere until immediately beforethe film formation.

End potions of the opening 521 of the second interlayer insulating film523 are preferably formed to be rounded. Thus, the light emitting layer512 partially overlapped with the interlayer insulating film 523 can beprevented from being broken at the end portions. Specifically, a radiusof curvature of a curve which is drawn by a cross section of the secondinterlayer insulating film in the opening is desirably in the range of0.2 μm to 2 μm approximately.

With the above structure, the coverage of the hole injection layer 511,the light emitting layer 512, and the electron injection layer 513 whichare to be formed later can be improved, and the pixel electrode 510 andthe electron injection layer 513 can be inhibited from being shortcircuited in a hole formed in the light emitting layer 512. Moreover, byalleviating the stress of the light emitting layer 512, a defect calledshrink in which a light emitting region is diminished can be suppressed,and thus, the reliability can be improved.

FIG. 14 shows an example of using a positive photosensitive acrylicresin as the second interlayer insulating film 523. A photosensitiveorganic resin includes a positive type in which a portion exposed to anenergy beam such as light, electrons, and ions is removed, and anegative type in which the exposed portion remains. In the invention, anegative photosensitive organic resin film may be used. Alternatively,the second interlayer insulating film 523 may be formed fromphotosensitive polyimide. When forming the second interlayer insulatingfilm 523 by using negative photosensitive acryl, a sectional shape ofthe end portions of the opening 521 has an S-like shape. Ai this time,the radius of curvature at the upper and the lower end portions of theopening are desirably in the range of 0.2 μn to 2 μm.

The first interlayer insulating film 507 or the second interlayerinsulating film 523 may be formed from a photosensitive organic resinused for a photoresist. In that case, for example, a solution obtainedby dissolving a cresol resin which is a kind of photosensitive organicresin into propylene glycolmonomethyl ether acetate (PGMEA) is appliedto the substrate, and the substrate is baked. Next, since the cresolresin is a positive photosensitive organic resin, the portion where anopening is to be formed is exposed by using a photomask. And after thedevelopment using a developing solution, the substrate is dried, bakingat 120° C. to 250° C. (for example, 125° C.) for approximately one houris performed thereafter; thus, the opening can be formed. Note that,before baking after the development, baking with slightly lowertemperature than the temperature of the baking (for example, around 100°C.) may be performed as pre-bake. The aspect ratio can be improved sothat the aperture of the contact hole to be provided in forming theconnection wiring 506 is small relative to its depth by using aphotosensitive organic resin for the first interlayer insulating film507. Further, when the above cresol resin is used for the firstinterlayer insulating film 507, moisture can be prevented from beingreleased from the first interlayer insulating film 507; accordingly, thepassivation film 508 is not necessary for suppressing deterioration ofthe light emitting element 514. Consequently, a short circuit betweenthe pixel electrode and the counter electrode caused by a dust which isgenerated from the silicon nitride film used for the passivation film508 can be prevented.

The second interlayer insulating film is not limited to the aboveorganic resin film and may be an inorganic insulating film, such assilicon oxide.

The pixel electrode 510 can be formed from not only ITO, IZO, or ITSObut also the transparent conductive film in which indium oxide is mixedwith tin oxide (ZnO) by 2% to 20% may be used. For the pixel electrode510, a titanium nitride film or a titanium film may be used other thanthe above transparent conductive film. In FIG. 4, ITO is used for thepixel electrode 510. The pixel electrode 510 may be polished by CMPmethod or by cleaning with a porous body of polyvinyl alcohol so thatthe surface of the pixel electrode 510 is made flat. Furthermore, thesurface of the pixel electrode 510 may be irradiated with an ultravioletray or may be treated with oxygen plasma after the CMP polishing.

FIGS. 4A to 4C show a configuration in which light emitted from thelight emitting element is released to the side of the substrate 500;however, another configuration in which light is emitted toward thedirection opposite to the substrate may be employed for the lightemitting element.

Having completed to the stage shown in FIGS. 4A to 4C, it is preferableto perform packaging (sealing) with a protective film (a laminated film,a UV curable resin film or the like) or a transparent cover materialwhich has high airtightness with a little degassing thereby avoidingexposure to the outside air. On this occasion, if the inside of thecover material is filled with an inert atmosphere or a hygroscopicmaterial (e.g., barium oxide) is provided inside, the reliability ofOLED is improved.

The invention is not limited to the fabrication method described above,and the light emitting element can be fabricated by using known methods.

In a light emitting device shown in FIGS. 4A to 4C, a protective film524 may have a layered structure of an inorganic insulating film and anorganic resin film. FIG. 22A shows a configuration in which theprotective film 524 shown in FIG. 4B has a layered structure. FIG. 22Bshows a configuration in which the protective film 524 shown in FIG. 4Chas a layered structure. In FIGS. 22A and 22B, an inorganic insulatingfilm 524 a is formed on the electron injection layer 513. An organicresin film 524 b and an inorganic insulating film 524 c are sequentiallystacked over the inorganic insulating film 524 a. A substance which mayaccelerate deterioration of a light emitting element such as moisture oroxygen can be prevented from entering the light emitting element 514 byusing silicon nitride, silicon oxynitride, aluminum oxide, aluminumnitride, aluminum nitride oxide, or aluminum silicide oxynitride is usedfor the inorganic insulating films 524 a and 524 c. Further, the organicresin film 524 b with less internal stress is provided between theinorganic insulating layers 524 a and 524 c; thus, the protective film524 can be prevented from being peeled off by stress. For the organicresin film 524 b, polyimide, acrylic, polyamide, polyimide amide,benzocyclobutene, or epoxy resin may be used.

In this embodiment mode, the electron injection layer 513 is coveredwith the protective film 524 as shown in FIG. 4; however, the inventionis not limited thereto. An example of forming a transparent conductivefilm between the electron injection layer 513 and the protective film524 in the light emitting device shown in FIGS. 4A to 4C is shown inFIGS. 5A to 5C. Note that, in FIGS. 5A to 5C, the same referencenumerals are used to refer to the like components which are alreadyshown in FIGS. 4A to 4C. Reference numeral 580 denotes a transparentconductive film. Even though the resistance of the electron injectionlayer 513 itself which serves as a counter electrode is increased, thepotential drop can be suppressed by forming the transparent conductivefilm 580 so as to be in contact with the electron injection layer 513.

In a light emitting device shown in FIGS. 4A to 4C, FIGS. 5A to 5C,FIGS. 22A and 22B, and FIGS. 23A and 23B; an electron injection layer isformed with a plurality of layers, and one of alkali metal, alkalineearth metal, and transition metal having the highest density is addedinto the electron injection layer of the top layer. FIG. 24 shows aconnection structure between an auxiliary electrode and a hole transportlayer in the case of providing two layers of electron injection layersin a light emitting device in FIGS. 4A to 4C. In FIG. 24, referencenumeral 659 denotes an opening for connecting a hole transport layer 654to an auxiliary electrode 660. Two layers of electron injection layers657 and 658 are formed and stacked sequentially over the hole transportlayer 654. Reference numeral 663 denotes a protective film. In FIG. 24,one of alkali metal, alkaline earth metal, and transition metal is addedto the electron injection layer 658 formed in the top layer with higherdensity than in the electron injection layer 657. Electron transportingmaterials for the electron injection layers 657 and 658 may be the sameor different.

Embodiment Mode 5

In this embodiment mode, an example of partially removing a holeinjection layer in the light emitting device shown in FIGS. 4A to 4C byplasma etching will be described. FIG. 6A shows a cross-sectional viewof a pixel of this embodiment mode. Further, enlarged views of theportions that are enclosed by dashed lines 601 and 602 in FIG. 6A arerespectively shown in FIGS. 6B and 6C.

In this embodiment mode, the configuration of a light emitting elementis the same as the configuration shown in FIGS. 4A to 4C. Specifically,a part of a pixel electrode 603 is exposed in an opening 605 formed in asecond interlayer insulating film 604. A hole injection layer 606, alight emitting layer 607, an electron injection layer 608, and aprotective film 613 are stacked sequentially over the pixel electrode603 so as to cover the opening 605. The protective film 613 is notnecessarily provided; however, deterioration of the light emittingelement can be reduced by providing the protective film. The portion inthe opening 605 where the pixel electrode 603, the hole injection layer606, the light emitting layer 607, and the electron injection layer 608overlap is a light emitting element 611.

Further, in the second interlayer insulating film 604, an opening 609for exposing a part of an auxiliary electrode 610 is formed other thanthe opening 605. In this embodiment mode, at least a part of theauxiliary electrode 610 is exposed so that the hole injection layer 606and the light emitting layer 607 do not completely cover up the opening609. Specifically, the auxiliary electrode 610 can be exposed byselectively etching the hole injection layer 606 and the light emittinglayer 607 by plasma etching using a metal mask 612. Alternatively, thelight emitting layer 607 may be selectively formed by vapor deposition,and the hole injection layer 606 may be selectively etched by plasmaetching.

With the above structure the auxiliary electrode 610 and the electroninjection layer 608 serving as a counter electrode can be connected inthe opening 609.

In a light emitting device shown in FIGS. 6A to 6C, a protective film613 may have a layered structure of an inorganic insulating film and anorganic resin film. FIG. 23A shows a configuration in which theprotective film 613 shown in FIG. 6B has a layered structure. FIG. 23Bshows a configuration in which the protective film 613 shown in FIG. 6Chas a layered structure. In FIGS. 23A and 23B, an inorganic insulatingfilm 613 a is formed on the electron injection layer 608, and an organicresin film 613 b and an inorganic insulating film 613 c are sequentiallystacked over the inorganic insulating film 613 a. A substance which mayaccelerate deterioration of a light emitting element such as moisture oroxygen can be prevented from entering the light emitting element 611 byusing silicon nitride, silicon oxynitride, aluminum oxide, aluminumnitride, aluminum nitride oxide, or aluminum silicide oxynitride is usedfor the inorganic insulating films 613 a and 613 c. Further, the organicresin film 613 b with less internal stress is provided between theinorganic insulating layers 613 a and 613 c; thus, the protective film613 can be prevented from being peeled off by stress. For the organicresin film 613 b, polyimide, acrylic, polyamide, polyimide amide,benzocyclobutene, or epoxy resin may be used.

In this embodiment mode, the electron injection layer 608 is coveredwith the protective film 613 as shown in FIG. 6; however, the inventionis not limited thereto. An example of forming a transparent conductivefilm between the electron injection layer 608 and the protective film613 in the light emitting device shown in FIGS. 6A to 6C is shown inFIGS. 7A to 7C. Note that, in FIGS. 7A to 7C, the same referencenumerals are used to refer to the like components which are alreadyshown in FIGS. 6A to 6C. Reference numeral 614 denotes a transparentconductive film. Even though the resistance of the electron injectionlayer 608 itself which serves as a counter electrode is increased, thepotential drop can be suppressed by forming the transparent conductivefilm 614 so as to be in contact with the electron injection layer 608.

Further, the opening 609 in a light emitting device shown in FIG. 7 isnot necessarily covered with the electron injection layer 608. Anexample of forming a transparent conductive film between the auxiliaryelectrode 610 and the protective film 613 in the light emitting deviceshown in FIGS. 7A to 7C is shown in FIGS. 8A to 8C. Note that, in FIG.8, the same reference numerals are used to refer to the like componentswhich are already shown in FIGS. 7A to 7C. Reference numeral 614 denotesa transparent conductive film. As shown in FIGS. 8A to 8C, thetransparent conductive film 614 and the auxiliary electrode 610 areconnected directly in the opening 609 by not covering the opening 609with the electron injection layer 608.

In a light emitting device shown in FIGS. 6A to 6C, FIGS. 7A to 7C, andFIGS. 8A to 8C, an electron injection layer is formed with a pluralityof layers, and one of alkali metal, alkaline earth metal, and transitionmetal having the highest density is added into an electron injectionlayer of the top layer as the light emitting device shown in FIG. 24.

Embodiment Mode 6

In this embodiment mode, connection between an auxiliary electrode andeach element provided in a pixel will be described.

A top view of a panel included in a light emitting device of theinvention is shown in FIG. 12. Reference numeral 700 denotes a substratein FIG. 12A. A signal line driver circuit 701, a scan line drivercircuit 702, and a pixel area 703 are provided over the substrate 700.An auxiliary electrode 705, a signal line 706, a scan line 707, and apower line 708 are provided in the pixel area 703. A video signal isgiven to the signal line 706 from the signal line driver circuit 701,and the potential of the scan line 707 is controlled by the scan linedriver circuit 702.

A plurality of connection terminals 704 are provided at the end portionof the substrate 700, and various signals and potentials are supplied tothe panel via the connection terminals 704. The potential given to eachof the auxiliary electrode 705 and the power line 708 is given from theconnection terminals 704 also via a leader wiring 709.

A schematic diagram of a pixel provided in the pixel area 703 is shownin FIG. 13A. Further, a part of the pixel area 703 in which the pixelsshown in FIG. 13A are arranged in matrix is shown in FIG. 13B.

A pixel shown in FIG. 13A includes two transistors of 801 and 802, alight emitting element 803, and a capacitor element 804. Further, thepixel includes a signal line S, a scan line G, a power line V, and anauxiliary electrode W. Reference numeral 801 denotes a transistor (aswitching transistor) for controlling input of a video signal to thepixel, and reference numeral 802 denotes a transistor (a drivertransistor) for controlling current supplied to the light emittingelement 803. Note that the capacitor element 804 has a function to keepthe potential of the gate electrode of the driver transistor 802 whenthe switching transistor 801 is off. The capacitor element is notnecessarily provided.

Specifically, as for the switching transistor 801, the gate electrode isconnected to the scan line G; one of the source and the drain isconnected to the signal line S; and the other is connected to the gateelectrode of the driver transistor 802. As for the driver transistor802, the source is connected to the power line V, and the drain isconnected to the pixel electrode of the light emitting element 803.Further, the counter electrode of the light emitting element 803 isconnected to the auxiliary electrode W. One of the two electrodes of thecapacitor element 804 is connected to the gate of the driver transistor802, and the other is connected to the power line V.

In FIG. 13B, an example of sharing the auxiliary electrode W in pixelssharing the signal line S and the power line V is shown. In the case ofFIG. 13B, the auxiliary electrode W can be formed from one conductivefilm from which the signal line S and the power line V are formed.

Further, an example of the auxiliary electrode W in pixels sharing thescan line G is shown in FIG. 14. In the case of FIG. 14, the auxiliaryelectrode W can be formed from one conductive film from which the scanline G is formed.

Note that the pixel shown in FIG. 13A only shows one embodiment of apixel included in a light emitting device of the invention, and a lightemitting device of the invention is not limited to the pixel shown inthis embodiment mode.

Embodiment 1

In this embodiment, a lay out of a leader wiring, an auxiliaryelectrode, a signal line, and a power line will be described.

A top view of a portion where a leader wiring and an auxiliary electrodeare connected is shown in FIG. 15. Reference numeral 1201 denotesconnection terminals, and the connection terminal is connected to awiring 1203 via a wiring 1202. Further, the wiring 1203 is connected toa wiring 1205 via a wiring 1204. The wiring 1205 is connected to anauxiliary electrode 1206; more specifically, the wiring 1205 is formedwith a conductive film shared by the auxiliary electrode 1206.Accordingly, in the case of FIG. 15, the leader wiring which connect theconnection terminals 1201 and the auxiliary electrode 1206 areequivalent to the wirings 1202, 1203, 1204, and 1205.

Reference numeral 1207 denotes a signal line driver circuit, and thesignal line driver circuit supplies a video signal to a signal line 1209via a wiring 1208. Power lines 1210 r, 1210 g, and 1210 b correspondingto each color are respectively connected to wirings 1212 r, 1212 g, and1212 b via wirings 1211 r, 1211 g, and 1211 b. The wiring 1212 b isfurther connected to a wiring 1214 via a wiring 1213. Wirings 1212 r,1212 g, and 1214 are respectively connected to connection terminals 1215r, 1215 g, and 1215 b.

Reference numeral 1216 denotes an opening formed in a second interlayerinsulating film, and in the opening 1216, the wiring 1205 and a counterelectrode (not shown) are connected directly or electrically.

Embodiment 2

In this embodiment, variations on a pixel of the invention will bedescribed.

FIG. 16A shows an example of a pixel included in the light emittingdevice of the invention. The pixel shown in FIG. 16A has a lightemitting element 901, a transistor used as a switching element forcontrolling a video signal inputted to the pixel, a driver transistor903 for controlling a current value supplied to the light emittingelement 901, and a current control transistor 904 for selecting whethercurrent is supplied to the light emitting element 901 or not. The pixelmay also have a capacitor element 905 for holding a potential of a gateof the transistor 904 as shown in this embodiment mode.

The switching transistor 902 may be either n-type or p-type. The drivertransistor 903 and the current control transistor 904 may be eithern-type or p-type, on condition that both of them has the sameconductivity type. The driver transistor 903 is operated in a saturationregion, and the current control transistor 904 is operated in a linearregion. Either an enhancement mode transistor or a depletion modetransistor may be used for the driver transistor 903.

The channel length L of the driver transistor 903 is preferably longerthan the channel width W thereof, and the channel length L of thecurrent control transistor 904 is preferably equal to or shorter thanthe channel width W thereof. More preferably, the ratio of the length Lto the width W of the driver transistor 903 is five or more. With theabove structure, variations in luminance of the light emitting element901 among pixels due to variations in characteristics of the drivertransistor 903 can be suppressed. Furthermore, assuming that L of thedriver transistor is L1 and W thereof is W1, and L of the currentcontrol transistor is L2 and W thereof is W2; when L1/W1:L2/W2=X:1 issatisfied, X is desirably in the range from 5 to 6000. For example, itis desirable that L1/W1=500 μm/3 μm, and L2/W2=3 μm/100 μm.

The gate electrode of the switching transistor 902 is connected to ascan line G. Either the source or drain of the switching transistor 902is connected to a signal line S, and the other is connected to the gateof the current control transistor 904. The gate electrode of the drivertransistor 903 is connected to a second power line Vb. The drivertransistor 903 and the current control transistor 904 are respectivelyconnected to the first power line Va and the light emitting element 901so that current supplied from the first power line Va is supplied to thelight emitting element 901 as a drain current of the driver transistor903 and of the current control transistor 904. In this embodiment thesource of the current control transistor 904 is connected to the firstpower line Va and the drain of the driver transistor 903 is connected toa pixel electrode of the light emitting element 901.

The source of the driver transistor 903 may be connected to the firstpower line Va, and the drain of the current control transistor 904 maybe connected to the pixel electrode of the light emitting element 901.

The light emitting element 901 has an anode, a cathode, and anelectroluminescent layer interposed between the anode and the cathode.As shown in FIG. 16A, when the anode of the light emitting element 901is connected to the driver transistor 903, the anode serves as a pixelelectrode and the cathode serves as a counter electrode. Potentialdifference is given between the first power line Va and the counterelectrode so that a forward bias is applied between the anode and thecathode of the light emitting element 901. The counter electrode isconnected to an auxiliary electrode W.

One of the two electrodes of the capacitor element 905 is connected tothe first power line Va, and the other is connected to the gateelectrode of the current control transistor 904. The capacitor element905 is disposed so as to hold a potential difference between theelectrodes of the capacitor element 905 when the switching transistor902 is not selected (in OFF state). It is to be noted that although FIG.16A shows a configuration in which the capacitor element 905 isprovided, the invention is not limited thereto and another configurationwithout the capacitor element 905 may be employed instead.

In FIG. 16A, each of the driver transistor 903 and the current controltransistor 904 is p-channel type, and the drain of the driver transistor903 is connected to the anode of the light emitting element 901. On thecontrary, in the case where each of the driver transistor 903 and thecurrent control transistor 904 is n-channel type, the source of thedriver transistor 903 is connected to the cathode of the light emittingelement 901. In this case, the cathode of the light emitting element 901serves as a pixel electrode and the anode thereof serves as a counterelectrode.

In FIG. 16B, a schematic diagram of a pixel provided with a transistor(erasing transistor) 906 which forcibly turns off the current controltransistor 904 in a pixel shown in FIG. 16A is shown. In FIG. 16B, thesame reference numerals are referred to the like elements alreadydescribed in FIG. 16A. Note that a first scan line is denoted by Ga, anda second scan line is denoted by Gb thereby distinguishing between thetwo scan lines. A gate electrode of the erasing transistor 906 isconnected to the first scan line Ga, and one of a source and a drainthereof is connected to a gate electrode of the current controltransistor 904, and the other is connected to the first power line Va.The erasing transistor 906 may be either n-type or p-type.

In FIG. 16C, a schematic diagram of a pixel in which a source of thecurrent control transistor 904 together with the gate electrode of thedriver transistor 903 are connected to one power line V in a pixel shownin FIG. 16A is shown. In FIG. 16C, the same reference numerals denotethe like elements already described in FIG. 16A. As shown in FIG. 16C,when the source of the current control transistor 904 and the gate ofthe driver transistor 903 are connected to one common power line V, adepletion mode transistor is used for the driver transistor 903, and anormal enhancement mode transistor is used for transistors other thanthe driver transistor 903.

In FIG. 16D, a schematic diagram of a pixel provided with a transistor(erasing transistor) 906 which forcibly turns off the current controltransistor 904 in a pixel shown in FIG. 16C is shown. In FIG. 16D, thesame reference numerals denote the like elements already described inFIGS. 16A to 16C. A gate electrode of the erasing transistor 906 isconnected to the first scan line Ga, and one of a source and a drainthereof is connected to a gate electrode of the current controltransistor 904, and the other is connected to the power line V. Theerasing transistor 906 may be either n-type or p-type.

In FIG. 17A, a schematic diagram of a pixel in which a gate electrode ofthe driver transistor 904 is connected to the second scan line Gb in apixel shown in FIG. 16A is shown. In FIG. 17A, the same referencenumerals denote the like elements already described in FIG. 16A. Asshown in FIG. 17A, the light emission of a light emitting element 901can be forcibly finished regardless of information included in a videosignal by changing potential given to the gate electrode of a drivertransistor 903. Either an enhancement mode transistor or a depletionmode transistor may be used for the driver transistor 903.

In FIG. 17B, a schematic diagram of a pixel provided with a transistor(erasing transistor) 906 which forcibly turns off the current controltransistor 904 in a pixel shown in FIG. 17A is shown. In FIG. 17B, thesame reference numerals denote the like elements already described inFIGS. 16A to 16D and FIG. 17A. A gate electrode of the erasingtransistor 906 is connected to the second scan line Gb, and one of asource and a drain thereof is connected to a gate electrode of thecurrent control transistor 904, and the other is connected to the powerline V. The erasing transistor 906 may be either n-type or p-type.

In FIG. 17C, a schematic diagram of a pixel in which the gate electrodeof the driver transistor 903 and the gate electrode of the currentcontrol transistor 904 are connected in a pixel shown in FIG. 16A isshown. In FIG. 17C, the same reference numerals denote the like elementsalready described in FIG. 16A. As shown in FIG. 17C, when the gateelectrodes of the current control transistor 904 and the drivertransistor 903 are connected, a depletion mode transistor is used forthe driver transistor 903, and a normal enhancement mode transistor isused for transistors other than the driver transistor 903.

A structure of the pixel in which a current control transistor is notprovided is shown in FIG. 17D. In FIG. 17D, reference numeral 911denotes a light emitting element, 912 denotes a switching transistor,913 denotes a driver transistor, 915 denotes a capacitor element, and916 denotes an erasing transistor. As for the switching transistor 912,the gate electrode is connected to the first scan line Ga; one of thesource and the drain is connected to the signal line S; and the other isconnected to the gate electrode of the driver transistor 913. As for thedriver transistor 913, the source is connected to the power line V, andthe drain is connected to the pixel electrode of the light emittingelement 911. Further, the counter electrode of the light emittingelement 911 is connected to the auxiliary electrode W. A gate electrodeof the erasing transistor 916 is connected to the second scan line Gb,and one of a source and a drain thereof is connected to the gateelectrode of the driver transistor 913, and the other is connected tothe power line V.

Note that, a configuration of a pixel included in a light emittingdevice of the invention is not limited to the configuration shown inthis embodiment.

Embodiment 3

In this embodiment, a mode of a pixel shown in FIG. 16A will bedescribed. FIG. 18 shows a top view of a pixel of this embodiment.

Reference numeral 8001 denotes a signal line, 8002 denotes a first powerline, 8003 denotes a second power line, 8004 denotes a first scan line,8005 denotes a second scan line, and 8006 denotes an auxiliaryelectrode. In this embodiment, the signal line 8001, the first powerline 8002, the second power line 8003, and the auxiliary electrode 8006are formed from one conductive film, and the first scan line 8004 andthe second scan line 8005 are formed from one conductive film. Referencenumeral 8007 denotes a switching transistor, and a part of the firstscan line 8004 serves as its gate electrode. Reference numeral 8008denotes an erasing transistor, and a part of the second scan line 8005serves as its gate electrode. Reference numeral 8009 denotes a currentcontrol transistor, and 8010 denotes a driver transistor. An activelayer of the driver transistor 8010 snakes so that the L/W becomeslarger than that of the current control transistor 8009. Referencenumeral 8011 denotes a pixel electrode, and it is overlapped with anelectroluminescent layer and a counter electrode (neither of them isshown) in an opening 8012. The auxiliary electrode 8006 is connected tothe counter electrode in an opening 8013. Reference numeral 8014 denotesa capacitor element, and it is formed from a gate insulating filmprovided between the second power line 8003 and the current controltransistor 8009.

Note that the top view shown in this embodiment is only an example, andthe invention is, needless to say, not limited to this.

Embodiment 4

A transistor used in the invention may be formed from amorphous silicon.When forming a transistor by using amorphous silicon, the fabricationmethod can be simplified since a crystallization process is notnecessary, which contributes to the cost reduction. Note that, as for atransistor formed from amorphous silicon, a n-channel transistor is moresuitable for a pixel of a light emitting device than a p-channeltransistor as an n-channel transistor has higher mobility. In thisembodiment, a cross-sectional structure of a pixel using an n-channeldriver transistor will be described.

FIG. 19A shows a cross-sectional view of a pixel in which a drivertransistor 6001 is n-channel type and light emitted from a lightemitting element 6002 is transmitted to the side of an anode 6005. InFIG. 19A, a cathode 6003 of the light emitting element 6002 iselectrically connected to the driver transistor 6001, and anelectroluminescent layer 6004 and an anode 6005 are sequentially stackedover the cathode 6003. Any known material can be used for the cathode6003 as long as it is a conductive film having light reflectivity and asmall work function. For example, Ca, Al, CaF, MgAg, AlLi, or the likeis desirably used. The electroluminescent layer 6004 may have a singlelayer or a plurality of layers. When it includes a plurality of layers,an electron injection layer, an electron transport layer, a lightemitting layer, a hole transport layer, and a hole injection layer aresequentially stacked over the cathode 6003. Note that all the abovelayers are not necessarily provided. The anode 6005 may be formed from atransparent conductive film which transmits light, such as ITO or one inwhich zinc oxide is mixed to indium oxide at a concentration of 2% to20%.

The portion where the cathode 6003, the electroluminescent layer 6004,and the anode 6005 overlap is equivalent to the light emitting element6002. In the case of the pixel shown in FIG. 19A, light emitted from thelight emitting element 6002 is transmitted to the side of the anode 6005as shown by an outline arrow.

A part of an active layer of the driver transistor 6001 serves as aresistor 6009.

FIG. 19B shows a cross-sectional view of a pixel in which a drivertransistor 6011 is n-channel type and light emitted from a lightemitting element 6012 is transmitted to the side of a cathode 6013. InFIG. 19B, the cathode 6013 of the light emitting element 6012 is formedover a transparent conductive film 6017 which is electrically connectedto a drain of the driver transistor 6011, and an electroluminescentlayer 6014 and an anode 6015 are sequentially stacked over the cathode6013. A shielding film 6016 which reflects or shuts off light is formedso as to cover the anode 6015. A known material can be used for thecathode 6013 as long as it is a conductive film having a small workfunction as in FIG. 19A. The film is formed to have a thickness thinenough to transmit light. For example, Al having a thickness of 20 nmcan be used for the cathode 6013. The electroluminescent layer 6014 mayhave a single layer or multiple layers as shown in FIG. 19A. The anode6015 may be formed from a transparent conductive film although it is notrequired to transmit light. For the shielding film 6016, alight-reflective metal can be used for example; however, the inventionis not limited to a metal film. For example, a resin added with a blackpigment or the like can be used.

The portion where the cathode 6013, the electroluminescent layer 6014,and the anode 6015 overlap is equivalent to the light emitting element6012. In the case of the pixel shown in FIG. 19B, light emitted from thelight emitting element 6012 is transmitted to the side of the cathode6013 as shown by an outline arrow.

A part of an active layer of the driver transistor 6011 serves as aresistor 6019.

Note that an example in which the driver transistor is electricallyconnected to the light emitting element in this embodiment; however, acurrent control transistor may be interposed between the drivertransistor and the light emitting element.

Embodiment 5

In this embodiment, a cross-sectional view of a pixel in which a drivertransistor is p-channel type.

FIG. 20A shows a cross-sectional view of a pixel in which a drivertransistor 6021 is p-channel type and light emitted from a lightemitting element 6022 is transmitted to the side of an anode 6023. InFIG. 20A, an anode 6023 of the light emitting element 6022 iselectrically connected to the driver transistor 6021, and anelectroluminescent layer 6024 and a cathode 6025 are sequentiallystacked over the anode 6023. Any known material can be used for thecathode 6025 as long as it is a conductive film having lightreflectivity and a small work function. For example, Ca, Al, CaF, MgAg,AlLi, or the like is desirably used. The electroluminescent layer 6024may have a single layer or a plurality of layers. When it includes aplurality of layers, a hole injection layer, a hole transport layer, alight emitting layer, an electron transport layer, and an electroninjection layer are sequentially stacked over the anode 6023. Note thatall the above layers are not necessarily provided. The anode 6023 may beformed from a transparent conductive film which transmits light, such asITO or one in which zinc oxide is mixed to indium oxide at aconcentration of 2% to 20%.

The portion where the anode 6023, the electroluminescent layer 6024, andthe anode 6025 overlap is equivalent to the light emitting element 6022.In the case of the pixel shown in FIG. 20A, light emitted from the lightemitting element 6022 is transmitted to the side of the anode 6023 asshown by an outline arrow.

A part of an active layer of the driver transistor 6021 serves as aresistor 6029.

FIG. 20B shows a cross-sectional view of a pixel in which a drivertransistor 6031 is p-channel type and light emitted from a lightemitting element 6032 is transmitted to the side of a cathode 6035. InFIG. 20B, the anode 6033 of the light emitting element 6032 is formedover a wiring 6037 which is electrically connected to a drain of thedriver transistor 6031, and an electroluminescent layer 6034 and thecathode 6035 are sequentially stacked over the anode 6033. With theabove structure, although light transmits through the anode 6033, thelight is reflected by the wiring 6037. A known material can be used forthe anode 6035 as long as it is a conductive film having a small workfunction as in FIG. 20A. The film is formed to have a thickness thattransmits light. For example, Al having a thickness of 20 nm can be usedfor the cathode 6035. The electroluminescent layer 6034 may have asingle layer or multiple layers as shown in FIG. 20A. The anode 6033 maybe formed with a transparent conductive film although it is not requiredto transmit light. For the wiring 6037, a light-reflective metal can beused.

The portion where the anode 6033, the electroluminescent layer 6034, andthe cathode 6035 overlap is equivalent to the light emitting element6032. In the case of the pixel shown in FIG. 20B, light emitted from thelight emitting element 6032 is transmitted to the side of the cathode6035 as shown by an outline arrow.

A part of an active layer of the driver transistor 6031 serves as aresistor 6039.

Note that an example in which the driver transistor is electricallyconnected to the light emitting element in this embodiment; however, acurrent control transistor may be interposed between the drivertransistor and the light emitting element.

Embodiment 6

A cross-sectional structure of a pixel of a dual emission light emittingdevice of the invention will be described with reference to FIG. 21. Adriver transistor 9001 formed over a substrate 9000 is shown in FIG. 21.The driver transistor 9001 is covered with a first interlayer insulatingfilm 9002, and a wiring 9004 which is electrically connected to thedrain of the driver transistor 9001 is formed over the first interlayerinsulating film 9002 through a contact hole.

The wiring 9004 is connected to a pixel electrode 9006. A secondinterlayer insulating film 9005 is formed over the first interlayerinsulating film 9002 so as to cover the wiring 9004 and a part of thepixel electrode 9006. Each of the first interlayer insulating film 9002and the second interlayer insulating film 9005 may be formed with asingle layer or a plurality of layers of silicon oxide, silicon nitride,or silicon oxynitride formed by plasma CVD or spattering. A film inwhich a silicon oxynitride film having a higher mole fraction of oxygenthan nitrogen is stacked over a silicon oxynitride film having a highermole fraction of nitrogen than oxygen may be used for the firstinterlayer insulating film 9002 or the second interlayer film 9005.Alternatively, an organic resin film or an organic polysiloxane may beused for the first interlayer insulating film 9002 or the secondinterlayer film 9005.

The second interlayer insulating film 9005 has an opening. A lightemitting element 9011 is formed by overlapping the pixel electrode 9006,an electroluminescent layer 9009, and a cathode 9010 in the opening. Inthis embodiment, a transparent conductive film is formed so as to coverthe cathode 9010.

The electroluminescent layer 7009 has a single light emitting layer ormultiple layers including a light emitting layer. Further, a protectivefilm may be formed over a transparent conductive film 9012. In thiscase, the protective film uses a film which hardly transmits a substancewhich may accelerate deterioration of a light emitting element such asmoisture or oxygen compared with other insulating films. Typically, aDLC film, a carbon nitride film, a silicon nitride film formed by RFsputtering, or the like is desirably used for the protective film.Further, a laminate of the film which hardly transmits substances suchas moisture and oxygen, and a film which transmits substances such asmoisture and oxygen easily compared with the above film may also be usedfor the protective film.

The pixel electrode 9006 can use a transparent conductive film. Not onlyITO, IZO, or ITSO but also a film in which zinc (ZnO) oxide is mixedwith indium oxide by 2% to 20% may be used as a transparent conductivefilm. In FIG. 21, ITO is used for the pixel electrode 9006. The pixelelectrode 9006 may be polished by CMP method or by cleaning with porousbody of polyvinyl alcohol so that the surface of the pixel electrode9006 is made flat. Furthermore, the surface of the pixel electrode 9006may be irradiated with ultraviolet ray or may be treated with oxygenplasma after the CMP method.

The cathode 9010 is formed thin enough to transmit light (preferably, 5nm to 30 nm), and may be formed of any one of known conductive filmswith a small work function, preferably using a material such as Ca, Al,CaF, MgAg, and AlLi. Note that, in order to obtain light from thecathode, ITO whose work function is made smaller by adding Li may beused instead of reducing the thickness of the cathode. In the invention,any structure of the light emitting element may be adopted as long aslight is released from both sides of an anode and a cathode.

In practical steps, when the pixel has been completed to the stage shownin FIG. 21, it is preferable to perform packaging (sealing) with aprotective film (a laminated film, a UV curable resin film, or the like)or a transparent cover material which has high airtightness with alittle degassing thereby avoiding exposure to the outside air. On thisoccasion, if the inside of the cover material is filled with an inertatmosphere and a hygroscopic material (e.g., barium oxide) is providedinside, the reliability of OLED is improved. Further, in the invention,a color filter may be provided for the cover material.

Note that the invention is not limited to the aforementioned fabricationmethod, and other known methods can be employed.

Embodiment 7

In this embodiment, the appearance of a panel equivalent to an exampleof a light emitting device of the invention will be described withreference to FIGS. 25A and 25B. FIG. 25A is a top view of a panel inwhich a transistor and a light emitting element formed over a firstsubstrate are sealed between the first substrate and a second substratewith the use of a sealing material. FIG. 25B is a sectional view takenalong line A-A′ in FIG. 25A.

A sealing material 4005 is provided so as to surround a pixel area 4002,a signal line driver circuit 4003, and a scan line driver circuit 4004provided over a first substrate 4001. A second substrate 4006 providedover the pixel area 4002, the signal line driver circuit 4003, and thescan line driver circuit 4004. Thus, the pixel area 4002, the signalline driver circuit 4003, and the scan line driver circuit 4004 togetherwith a filler material 4007 are sealed by the first substrate 4001, thesealing material 4005, and the second substrate 4006.

The pixel area 4002, the signal line driver circuit 4003, and the scanline driver circuit 4004 provided over the first substrate 4001 have aplurality of transistors, and transistors 4008 and 4009 included in thesignal line driver circuit 4003 and a driver transistor 4010 included inthe pixel area 4002 are shown in FIG. 25B.

Further, reference numeral 4011 denotes a light emitting element, andthe pixel electrode 4011 included in the light emitting element iselectrically connected to the drain of the driver transistor 4010 viathe wiring 4017. In this embodiment, a counter electrode of the lightemitting element 4011 and a transparent conductive film 4012 areconnected electrically, and the transparent conductive film 4012 isconnected to an auxiliary electrode 4013 electrically. The auxiliaryelectrode 4013 is electrically connected to a connection terminal 4016via leader wirings 4014 and 4015, although this configuration is notshown in the cross-sectional view of FIG. 25B.

In this embodiment, a connection terminal 4016 is formed from aconductive film of a pixel electrode included in the light emittingelement 4011. The leader wiring 4014 is formed from a conductive filmforming the wiring 4017. Further, the leader wiring 4015 is formed froma conductive film also forming the gate electrode included in each ofthe driver transistor 4010 and the transistors 4008 and 4009.

The connection terminal 4016 is electrically connected to a terminal ofa FPC 4018 via an anisotropic conductive film 4019.

Glass, metal (typically, stainless), ceramic, or plastic may be used forthe first substrate 4001 and the second substrate 4006. As the plastic,an FRP (fiberglass-reinforced plastics) plate, a PVF (polyvinylfluoride) film, a Mylar film, a polyester film, or an acrylic resin filmmay be used. Further, a sheet with a structure in which an aluminum foilis sandwiched between PVF films or Mylar films may also be used.

However, the second substrate that is located in a side where the lightfrom the light emitting element 4011 is released is required to betransparent. In that case, a transparent material such as a glass plate,a plastic plate, a polyester film or an acrylic film is used.

Further, in addition to an inert gas such as nitrogen or argon, a UVcurable resin or a thermosetting resin may be used as the fillermaterial 4007, so that PVC (polyvinyl chloride), acrylic, polyimide,epoxy resin, silicon resin, PVB (polyvinyl butyral) or EVA (ethylenevinyl acetate) may be used. In this embodiment, nitrogen is used for thefiller material.

A hygroscopic material (preferably, barium oxide) or a material whichcan absorb oxygen may be provided to expose the filler material 4007thereto or to the substance that can absorb oxygen. The deterioration ofthe light emitting element 4011 can be suppressed by providing thehygroscopic material or the material which can absorb oxygen.

Embodiment 8

Since a light-emitting device using a light-emitting element emits lightby itself, it exhibits higher visibility in a bright place as comparedto a liquid crystal display device. Further, the light-emitting devicehas a wider viewing angle. Accordingly, the light-emitting device can beapplied to a display area in various electronic devices.

Electronic devices using such a light-emitting device of the presentinvention include a video camera, a digital camera, a goggle display(head mounted display), a navigation system, a sound reproduction device(a car audio equipment and an audio set), a notebook personal computer,a game machine, a PDA (a Portable Digital Assistant, e.g. a mobilecomputer, a cellular phone, a portable game machine, an electronic book,or the like), an image reproduction device including a recording medium(more specifically, a device which can reproduce a recording medium suchas a digital versatile disc (DVD) and so forth, and includes a displayfor displaying the reproduced image), or the like. In particular, in thecase of the PDA, it is preferable to use a light-emitting device, sincethe PDA which is often viewed from a an angle and is required to have awide viewing angle. FIGS. 26A to 26E respectively show various specificexamples of such electronic devices.

FIG. 26A shows a PDA including a main body 2001, a display area 2002, anoperation key 2003, and a modem 2004. The modem 2004 of the PDA shown inFIG. 26A is detachable; however, a modem may be included in the mainbody 2001. A light emitting device of the invention can be applied tothe display area 2002.

FIG. 26B shows a cellular phone including a main body 2101, a displayarea 2102, an audio input part 2103, an audio output part 2104, anoperation key 2105, an external connection port 2106, and an antenna2107. The current consumption of the cellular phone can be reduced bydisplaying white letters on black background in the display area 2102. Alight emitting device of the invention can be applied to the displayarea 2102.

FIG. 26C shows an electronic card including a main body 2201, a displayarea 2202, and a connection terminal 2203. A light emitting device ofthe invention can be applied to the display area 2202. A contactelectronic card is shown in FIG. 26C; however, a light emitting deviceof the invention can be applied to a contactless electronic card, or toan electronic card which has functions of both contact type andcontactless type.

FIG. 26D shows an electronic book including a main body 2301, a displayarea 2302, and an operation key 2303. Further, a modem may be includedin the main body 2301. A light emitting device of the invention can beapplied to the display area 2302.

FIG. 26E shows a sheet personal computer including a main body 2401, adisplay area 2402, a keyboard 2403, a touch pad 2404, an externalconnections port 2405, and a power plug 2406. A light emitting device ofthe invention can be applied to the display area 2402.

As described above, the application range of the invention is extremelywide, and the invention can be applied to an electronic device in allfields. Further, an electronic device described in this embodiment mayuse a light emitting device having a structure shown in any one ofEmbodiments 1 through 7.

1. A light emitting device comprising: an insulating film; a lightemitting element in a pixel; and an auxiliary electrode in the pixel,wherein the light emitting element formed in a first opening formed inthe insulating film, comprises: a first electrode; a second electrodeover the first electrode and the insulating film; and anelectroluminescent layer provided between the first and the secondelectrodes, and wherein the auxiliary electrode is in contact with thesecond electrode in a second opening formed in the insulating film.
 2. Alight emitting device comprising: a first insulating film; a firstelectrode over the first insulating film; an auxiliary electrode overthe first insulating film; a second insulating film having a firstopening and a second opening over the first insulating film; anelectroluminescent layer formed over the second insulating filmso as tocover the first and the second openings; and a second electrode incontact with the electroluminescent layer, wherein theelectroluminescent layer is in contact with the first electrode in thefirst opening, and wherein the electroluminescent layer is in contactwith a top surface of the auxiliary electrode and the second electrodeis in contact with a side surface of the auxiliary electrode in thesecond opening.
 3. A light emitting device comprising: a firstinsulating film; an anode over the first insulating film; an auxiliaryelectrode over the first insulating film; a second insulating filmhaving a first opening and a second opening over the first insulatingfilm; an electroluminescent layer formed over the second insulating filmso as to cover the first and the second openings; and an electroninjection layer in contact with the electroluminescent layer, whereinthe electroluminescent layer is in contact with the anode in the firstopening, and wherein the electroluminescent layer is in contact with atop surface of the auxiliary electrode and the electron injection layeris in contact with a side surface of the auxiliary electrode in thesecond opening.
 4. A light emitting device comprising: a firstinsulating film; a first electrode over the first insulating film; anauxiliary electrode over the first insulating film; a second insulatingfilm having a first opening and a second opening over the firstinsulating film; an electroluminescent layer formed over the secondinsulating film so as to cover the first opening; and a second electrodein contact with the electroluminescent layer and to cover the secondopening, wherein the electroluminescent layer is in contact with thefirst electrode in the first opening, and wherein the auxiliaryelectrode and the second electrode are in contact with each other in thesecond opening.
 5. A light emitting device comprising: a firstinsulating film; an anode over the first insulating film; an auxiliaryelectrode over the first insulating film; a second insulating filmhaving a first opening and a second opening over the first insulatingfilm; a light emitting layer formed over the second insulating film soas to cover the first opening of the first and the second openings; andan electron injection layer in contact with the light emitting layer andto cover the second opening, wherein the light emitting layer is incontact with the anode in the first opening, and wherein the auxiliaryelectrode and the electron injection layer are in contact with eachother in the second opening.
 6. A light emitting device according toclaim 3, wherein the electron injection layer uses a benzoxazolederivative added with one selected from the group consisting of analkali metal, an alkaline earth metal, and a transition metal.
 7. Alight emitting device according to claim 5, wherein the electroninjection layer uses a benzoxazole derivative added with one selectedfrom the group consisting of an alkali metal, an alkaline earth metal,and a transition metal.
 8. A light emitting device according to claim 6,wherein the molar ratio of the benzoxazole derivative and one selectedfrom the group consisting of an alkali metal, an alkaline earth metal,and a transition metal is 1:0.1 to 1:10 in the electron injection layer.9. A light emitting device according to claim 7, wherein the molar ratioof the benzoxazole derivative and one selected from the group consistingof an alkali metal, an alkaline earth metal, and a transition metal is1:0.1 to 1:10 in the electron injection layer.
 10. A light emittingdevice according to claim 1, wherein the first insulating film comprisesa photosensitive organic resin.
 11. A light emitting device according toclaim 2, wherein the first insulating film comprises a photosensitiveorganic resin.
 12. A light emitting device according to claim 3, whereinthe first insulating film comprises a photosensitive organic resin. 13.A light emitting device according to claim 4, wherein the firstinsulating film comprises a photosensitive organic resin.
 14. A lightemitting device according to claim 5, wherein the first insulating filmcomprises a photosensitive organic resin.
 15. A light emitting deviceaccording to claim 10, wherein the photosensitive resin includes acresol resin.
 16. A light emitting device according to claim 11, whereinthe photosensitive resin includes a cresol resin.
 17. A light emittingdevice according to claim 12, wherein the photosensitive resin includesa cresol resin.
 18. A light emitting device according to claim 13,wherein the photosensitive resin includes a cresol resin.
 19. A lightemitting device according to claim 14, wherein the photosensitive resinincludes a cresol resin.
 20. A light emitting device according to claim1, wherein the second electrode is a transparent conductive film.
 21. Alight emitting device according to claim 2, wherein the second electrodeis a transparent conductive film.
 22. A light emitting device accordingto claim 4, wherein the second electrode is a transparent conductivefilm.
 23. A light emitting device according to claim 1, furthercomprising: a transparent conductive film over the second electrode; anda protective film over the transparent conductive film.
 24. A lightemitting device according to claim 2, further comprising: a transparentconductive film over the second electrode; and a protective film overthe transparent conductive film.
 25. A light emitting device accordingto claim 3, further comprising: a transparent conductive film over theelectron injection layer; and a protective film over the transparentconductive film.
 26. A light emitting device according to claim 4,further comprising: a transparent conductive film over the secondelectrode; and a protective film over the transparent conductive film.27. A light emitting device according to claim 5, further comprising: atransparent conductive film over the electron injection layer; and aprotective film over the transparent conductive film.
 28. An electronicdevice comprising the light emitting device according to claim
 1. 29. Anelectronic device comprising the light emitting device according toclaim
 2. 30. An electronic device comprising the light emitting deviceaccording to claim
 3. 31. An electronic device comprising the lightemitting device according to claim
 4. 32. An electronic devicecomprising the light emitting device according to claim
 5. 33. Anelectronic device according to claim 28, wherein the electronic deviceis selected from the group consisting of a PDA, a cellular phone, anelectronic card, an electronic book and a personal computer.
 34. Anelectronic device according to claim 29, wherein the electronic deviceis selected from the group consisting of a PDA, a cellular phone, anelectronic card, an electronic book and a personal computer.
 35. Anelectronic device according to claim 30, wherein the electronic deviceis selected from the group consisting of a PDA, a cellular phone, anelectronic card, an electronic book and a personal computer.
 36. Anelectronic device according to claim 31, wherein the electronic deviceis selected from the group consisting of a PDA, a cellular phone, anelectronic card, an electronic book and a personal computer.
 37. Anelectronic device according to claim 32, wherein the electronic deviceis selected from the group consisting of a PDA, a cellular phone, anelectronic card, an electronic book and a personal computer.
 38. Amethod for fabricating a light emitting device, comprising: forming awiring and an auxiliary electrode over a first insulating film; forminga first electrode over the first insulating film so as to be in contactwith the wiring; forming a second insulating film over the firstinsulating film so as to cover the first electrode, the wiring, and theauxiliary electrode; forming a first opening for exposing the firstelectrode and a second opening for exposing the auxiliary electrode inthe second insulating film; forming an electroluminescent layer over thesecond insulating film so as to cover the first and the second openings;and forming a second electrode so as to be in contact with theelectroluminescent layer; wherein the electroluminescent layer is incontact with the first electrode in the first opening, and wherein theelectroluminescent layer is in contact with a top surface of theauxiliary electrode and the second electrode is in contact with a sidesurface of the auxiliary electrode in the second opening.
 39. A methodfor fabricating a light emitting device, comprising: forming a firstelectrode over a first insulating film; forming an auxiliary electrodeand a wiring which is in contact with a part of the first electrode overthe first insulating film; forming a second insulating film over thefirst insulating film so as to cover the first electrode, the wiring,and the auxiliary electrode; forming a first opening for exposing thefirst electrode and a second opening for exposing the auxiliaryelectrode in the second insulating film; forming an electroluminescentlayer over the second insulating film so as to cover the first and thesecond openings; and forming a second electrode so as to be in contactwith the electroluminescent layer, wherein the electroluminescent layeris in contact with the first electrode in the first opening, and whereinthe electroluminescent layer is in contact with a top surface of theauxiliary electrode and the second electrode is in contact with a sidesurface of the auxiliary electrode in the second opening.
 40. A methodfor fabricating a light emitting device, comprising: forming a wiringand an auxiliary electrode over a first insulating film; forming a firstelectrode over the first insulating film so as to be in contact with thewiring; forming a second insulating film over the first insulating filmso as to cover the first electrode, the wiring, and the auxiliaryelectrode; forming a first opening for exposing the first electrode anda second opening for exposing the auxiliary electrode in the secondinsulating film; forming an electroluminescent layer over the secondinsulating film so as to cover the first opening; and forming a secondelectrode so as to be in contact with the electroluminescent layer andto cover the second opening, wherein the electroluminescent layer is incontact with the first electrode in the first opening, and wherein theauxiliary electrode and the second electrode are in contact with eachother in the second opening.
 41. A method for fabricating a lightemitting device, comprising: forming a first electrode over a firstinsulating film; forming an auxiliary electrode and a wiring which is incontact with a part of the first electrode over the first insulatingfilm; forming a second insulating film over the first insulating film soas to cover the first electrode, the wiring, and the auxiliaryelectrode; forming a first opening for exposing the first electrode anda second opening for exposing the auxiliary electrode in the secondinsulating film; forming an electroluminescent layer over the secondinsulating film so as to cover the first opening; and forming a secondelectrode so as to be in contact with the electroluminescent layer andto cover the second opening, wherein the electroluminescent layer is incontact with the first electrode in the first opening, and wherein theexposed auxiliary electrode and the second electrode are in contact witheach other in the second opening.
 42. A method for fabricating a lightemitting device according to claim 38, wherein the first insulating filmis formed from a photosensitive organic resin.
 43. A method forfabricating a light emitting device according to claim 39, wherein thefirst insulating film is formed from a photosensitive organic resin. 44.A method for fabricating a light emitting device according to claim 40,wherein the first insulating film is formed from a photosensitiveorganic resin.
 45. A method for fabricating a light emitting deviceaccording to claim 41, wherein the first insulating film is formed froma photosensitive organic resin.
 46. A method for fabricating a lightemitting device according to claim 42, wherein the photosensitive resinincludes a cresol resin.
 47. A method for fabricating a light emittingdevice according to claim 43, wherein the photosensitive resin includesa cresol resin.
 48. A method for fabricating a light emitting deviceaccording to claim 44, wherein the photosensitive resin includes acresol resin.
 49. A method for fabricating a light emitting deviceaccording to claim 45, wherein the photosensitive resin includes acresol resin.
 50. A method for fabricating a light emitting deviceaccording to claim 38, wherein the electroluminescent layer is formed byvapor deposition.
 51. A method for fabricating a light emitting deviceaccording to claim 39, wherein the electroluminescent layer is formed byvapor deposition.
 52. A method for fabricating a light emitting deviceaccording to claim 40, wherein the electroluminescent layer is formed byvapor deposition.
 53. A method for fabricating a light emitting deviceaccording to claim 41, wherein the electroluminescent layer is formed byvapor deposition.
 54. A light emitting device comprising: a thin filmtransistor over an insulating surface, comprising: a semiconductor filmcomprising; a channel forming region; a source region; and a drainregion; a first insulating film over the thin film transistor; aconductive wiring over the first insulating film and connected to thedrain region of the thin film transistor through a contact hole; a firstelectrode over the first insulating film and connected to the conductivewiring; an auxiliary electrode over the first insulating film; a secondinsulating film having a first opening and a second opening over thefirst insulating film; an electroluminescent layer formed over thesecond insulating filmso as to cover the first and the second openings;and a second electrode in contact with the electroluminescent layer,wherein the electroluminescent layer is in contact with the firstelectrode in the first opening, and wherein the electroluminescent layeris in contact with a top surface of the auxiliary electrode and thesecond electrode is in contact with a side surface of the auxiliaryelectrode in the second opening.
 55. A light emitting device comprising:a thin film transistor over an insulating surface, comprising: asemiconductor film comprising: a channel forming region; a sourceregion; and a drain region; a first insulating film over the thin filmtransistor; a conductive wiring over the first insulating film andconnected to the drain region of the thin film transistor through acontact hole; an anode over the first insulating film; an auxiliaryelectrode over the first insulating film; a second insulating filmhaving a first opening and a second opening over the first insulatingfilm; an electroluminescent layer formed over the second insulating filmso as to cover the first and the second openings; and an electroninjection layer in contact with the electroluminescent layer, whereinthe electroluminescent layer is in contact with the anode in the firstopening, and wherein the electroluminescent layer is in contact with atop surface of the auxiliary electrode and the electron injection layeris in contact with a side surface of the auxiliary electrode in thesecond opening.
 56. A light emitting device comprising: a thin filmtransistor over an insulating surface, comprising; a semiconductor filmcomprising; a channel forming region; a source region; and a drainregion; a first insulating film over the thin film transistor; aconductive wiring over the first insulating film and connected to thedrain region of the thin film transistor through a contact hole; a firstelectrode over the first insulating film and connected to the conductivewiring; an auxiliary electrode over the first insulating film; a secondinsulating film having a first opening and a second opening over thefirst insulating film; an electroluminescent layer formed over thesecond insulating film so as to cover the first opening; and a secondelectrode in contact with the electroluminescent layer and to cover thesecond opening, wherein the electroluminescent layer is in contact withthe first electrode in the first opening, and wherein the auxiliaryelectrode and the second electrode are in contact with each other in thesecond opening.
 57. A light emitting device comprising: a thin filmtransistor over an insulating surface, comprising: a semiconductor filmcomprising: a channel forming region; a source region; and a drainregion; a first insulating film over the thin film transistor; aconductive wiring over the first insulating film and connected to thedrain region of the thin film transistor through a contact hole; ananode over the first insulating film; an auxiliary electrode over thefirst insulating film; a second insulating film having a first openingand a second opening over the first insulating film; a light emittinglayer formed over the second insulating film so as to cover the firstopening of the first and the second openings; and an electron injectionlayer in contact with the light emitting layer and to cover the secondopening, wherein the light emitting layer is in contact with the anodein the first opening, and wherein the auxiliary electrode and theelectron injection layer are in contact with each other in the secondopening.
 58. A light emitting device according to claim 54, wherein thefirst electrode is overlapped partially or entirely with the conductivewiring and formed over and in contact with the conductive wiring.
 59. Alight emitting device according to claim 55, wherein the anode isoverlapped partially or entirely with the conductive wiring and formedover and in contact with the conductive wiring.
 60. A light emittingdevice according to claim 56, wherein the first electrode is overlappedpartially or entirely with the conductive wiring and formed over and incontact with the conductive wiring.
 61. A light emitting deviceaccording to claim 57, wherein the anode is overlapped partially orentirely with the conductive wiring and formed over and in contact withthe conductive wiring.
 62. A light emitting device according to claim54, wherein the first electrode is overlapped partially or entirely withthe conductive wiring and formed under and in contact with theconductive wiring.
 63. A light emitting device according to claim 55,wherein the anode is overlapped partially or entirely with theconductive wiring and formed under and in contact with the conductivewiring.
 64. A light emitting device according to claim 56, wherein thefirst electrode is overlapped partially or entirely with the conductivewiring and formed under and in contact with the conductive wiring.
 65. Alight emitting device according to claim 57, wherein the anode isoverlapped partially or entirely with the conductive wiring and formedunder and in contact with the conductive wiring.
 66. A light emittingdevice according to claim 55, wherein the electron injection layer usesa benzoxazole derivative added with one selected from the groupconsisting of an alkali metal, an alkaline earth metal, and a transitionmetal.
 67. A light emitting device according to claim 57, wherein theelectron injection layer uses a benzoxazole derivative added with oneselected from the group consisting of an alkali metal, an alkaline earthmetal, and a transition metal.
 68. A light emitting device according toclaim 66, wherein the molar ratio of the benzoxazole derivative and oneselected from the group consisting of an alkali metal, an alkaline earthmetal, and a transition metal is 1:0.1 to 1:10 in the electron injectionlayer.
 69. A light emitting device according to claim 67, wherein themolar ratio of the benzoxazole derivative and one selected from thegroup consisting of an alkali metal, an alkaline earth metal, and atransition metal is 1:0.1 to 1:10 in the electron injection layer.
 70. Alight emitting device according to claim 54, wherein the firstinsulating film comprises a photosensitive organic resin.
 71. A lightemitting device according to claim 55, wherein the first insulating filmcomprises a photosensitive organic resin.
 72. A light emitting deviceaccording to claim 56, wherein the first insulating film comprises aphotosensitive organic resin.
 73. A light emitting device according toclaim 57, wherein the first insulating film comprises a photosensitiveorganic resin.
 74. A light emitting device according to claim 70,wherein the photosensitive resin includes a cresol resin.
 75. A lightemitting device according to claim 71, wherein the photosensitive resinincludes a cresol resin.
 76. A light emitting device according to claim72, wherein the photosensitive resin includes a cresol resin.
 77. Alight emitting device according to claim 73, wherein the photosensitiveresin includes a cresol resin.
 78. A light emitting device according toclaim 54, wherein the second electrode is a transparent conductive film.79. A light emitting device according to claim 56, wherein the secondelectrode is a transparent conductive film.
 80. A light emitting deviceaccording to claim 54, further comprising: a transparent conductive filmover the second electrode; and a protective film over the transparentconductive film.
 81. A light emitting device according to claim 55,further comprising: a transparent conductive film over the electroninjection layer; and a protective film over the transparent conductivefilm.
 82. A light emitting device according to claim 56, furthercomprising: a transparent conductive film over the second electrode; anda protective film over the transparent conductive film.
 83. A lightemitting device according to claim 57, further comprising: a transparentconductive film over the electron injection layer; and a protective filmover the transparent conductive film.
 84. An electronic devicecomprising the light emitting device according to claim
 54. 85. Anelectronic device comprising the light emitting device according toclaim
 55. 86. An electronic device comprising the light emitting deviceaccording to claim
 56. 87. An electronic device comprising the lightemitting device according to claim
 57. 88. An electronic deviceaccording to claim 84, wherein the electronic device is selected fromthe group consisting of a PDA, a cellular phone, an electronic card, anelectronic book and a personal computer.
 89. An electronic deviceaccording to claim 85, wherein the electronic device is selected fromthe group consisting of a PDA, a cellular phone, an electronic card, anelectronic book and a personal computer.
 90. An electronic deviceaccording to claim 86, wherein the electronic device is selected fromthe group consisting of a PDA, a cellular phone, an electronic card, anelectronic book and a personal computer.
 91. An electronic deviceaccording to claim 87, wherein the electronic device is selected fromthe group consisting of a PDA, a cellular phone, an electronic card, anelectronic book and a personal computer.